1. Field of the Invention
This invention relates to an apparatus for cleaning the interior wall of a pipeline carrying a petroleum oil or hydrocarbon gas that tends to deposit a wax-like layer on said interior wall, and more particularly concerns a pipeline cleaning apparatus that can be controllably advanced by fluid pressure applied through said pipeline upon said apparatus.
2. Description of the Prior Art
Solids such as paraffin wax and related viscous products tend to deposit on the interior wall of oil and gas pipelines, and the accumulation of such deposits is accelerated by cold temperatures. Mechanical cleaning devices, commonly called pigs, are often used to clean such pipelines. Pigs are generally plugs that can slide through the pipeline by the force of fluids behind the pig, removing undesirable materials by pushing these materials in front of the pig. In long pipelines, stations to launch and catch these pigs are typically provided in the pipeline.
A problem when using a pig is that the debris dislodged from the interior wall as the pig progresses through the pipeline can accumulate and block further motion of the pig. This phenomenon is aggravated with increased speed of the pig. Such blockage requires expensive remediation in terms of locating and accessing the site of blockage, cutting the pipeline, removing the pig and the blocking accumulation, and re-welding the pipeline. Such remediation is particularly costly with undersea pipelines.
In order to minimize the accumulation of debris in front of the advancing pig, rotating nozzles have been mounted on the forward extremity of the pig for directing high velocity fluid jets toward the interior pipe wall. The jets dislodge the debris and break it into relatively small pieces which are flushed forwardly away from the pig. The energy required to rotate the nozzles is provided by a pressurized upstream activating liquid, which may be water. Activating liquid pressures in the range of 400-500 psi may be employed, and are suitable for rotating the nozzle and advancing the pig. The high velocity jets are produced by hydraulic pressure intensifiers within the pig that generate pressures at the nozzle which are considerably greater than the pressure of the activating liquid.
It is necessary to control the rate of forward movement of the pig. One earlier disclosed technique for controlling the movement of the pig, and facilitating its retrieval in the event of a blockage, has involved the use of a tether cable. However, use of a cable restricts the length of pipeline that can be cleaned because of the weight of an extended length of cable. For example, a pipeline having a length of greater than about a mile would be very difficult to clean with a tether cable. Further, a tensioner and a seal must be provided around the cable where the cable enters the pipeline. This seal provides an opportunity for pipeline contents to escape, resulting in unwanted emissions.
In pig systems utilizing a pressurized upstream activating fluid, various techniques have been described for enabling the pressure of the activating liquid to operate a braking mechanism on the pig so as to control forward movement. For example, U.S. Pat. No. 5,875,803 to Leitko, et. al. discloses the use of a coil spring that fits closely within the pipeline and which elongates in response to pressure, thereby causing a narrowing of the diameter of the spring with attendant release from gripping engagement of the interior surface of the pipeline. Leitko, et. al. also discloses a braking mechanism in the form of brake pads urged against said inside surface by suitable pressure differential.
U.S. Patent to Geppert discloses a pig having a brake mechanism energized by a pressurized activating fluid in a manner such that force is exerted upon clamping shoes interactive with the pipe wall. The intensity of said braking force increases with increased forward motion of the pig.
The braking systems of Leitko, et. al. and Geppert are based upon rigid mechanical structures that are forced against circumferentially spaced sites on the interior of the pipe. Although functionally reliable on a clean pipe surface, their reliability diminishes on surfaces of varying cleanliness because of the unpredictable interaction of the rigid brake pads with surface irregularities at randomly spaced sites. Such prior pig devices also do not clearly address the need for increasing the pressure of the activating liquid for energizing the braking mechanism, and for producing jets of sufficiently high velocity to remove the deposits.
It is accordingly an object of the present invention to provide apparatus with reliable braking means for use in removing solids from the inside surface of conduits.
It is another object of this invention to provide apparatus as in the foregoing object that employs high velocity liquid jets to remove said solids and flush them downstream through said conduit.
It is a further object of the present invention to provide apparatus of the aforesaid nature for use in conjunction with a pressurized upstream liquid for removing solids from the inside surface of a conduit.
It is yet another object of this invention to provide apparatus of the aforesaid nature having the ability to produce hydraulic pressures greater than the pressure of said upstream liquid for operating said braking means and producing said high velocity jets.
These objects and other objects and advantages of the invention will be apparent from the following description.